I've got the sip-communicator up and running be I'm having a lot of
problems with it. It connects a SIP Call across my internal network
but fails to set up any media at all.

I've now tried to use a Proxy in the network (Sip Express Router) and
I've told it the address of the Proxy bit it seems to be looking for a
proxy at a different address. Has anybody had any expierence of using
the sip-communicator and getting it working with a proxy?